Erythromycins A through D are represented by the following formula: ##STR1##
______________________________________ Erythromycin R' R' ' ______________________________________ A --OH --CH.sub.3 B --H --CH.sub.3 C --OH --H D --H --H ______________________________________ and are well-known and potent antibacterial agents. These compounds are used widely to treat and prevent bacterial infection. As with other antibacterial agents, however, bacterial strains having resistance or insufficient susceptibility to erythromycin have been identified. Erythromycin A has only weak activity against Gram-negative bacteria. Therefore, there is a continuing need to identify new macrolide compounds which possess improved antibacterial activity, which have less potential for developing resistance, which possess the desired Gram-negative activity, and/or which possess unexpected selectivity against target microorganisms. Consequently, numerous investigators have prepared chemical derivatives of erythromycin in an attempt to obtain analogs having modified or improved profiles of antibiotic activity.
U.S. Pat. No. 5,444,051 discloses 6-O-substituted-3-oxoerythromycin A derivatives in which the substituents are selected from alkyl, --CONH.sub.2, --CONHC(O)alkyl and --CONHSO.sub.2 alkyl. WO 97/10251, published Mar. 20, 1997, discloses 6-O-methyl 3-descladinose erythromycin derivatives. European Patent Application 596802, published May 11, 1994, discloses bicyclic 6-O-methyl-3-oxoerythromycin A derivatives. WO 92/09614, published Jun. 11, 1992, discloses tricyclic 6-O-methylerythromycin A derivatives.